1. Field of the Invention
The present invention relates generally to the art of electrochemical cells and more particularly to a cell design for use under high shock and vibration conditions.
Electrochemical cells are used frequently in applications where high shock and vibration levels are experienced. A notable example is in the gas and oil industry where "measurement while drilling" applications utilize nonaqueous cells of both solid and liquid cathode chemistries. Preferred are lithium cells. Under high shock and vibration conditions, cells without adequate stabilization are capable of failing due to movement of the cell stack or electrode assembly within the case. This movement can result in the mechanical failure of the electrode leads rendering the cell inoperative or, in the worst case, may produce a short circuit within the cell. In that respect, mechanical stabilization of the electrode assembly inside the cell case is important to improving the reliability and safety of electrochemical cells subjected to high shock and vibration conditions.
The electrochemical cell of the present invention provides such mechanical stabilization through a plurality of tab means electrically connecting at least one of the positive and negative electrodes to the cell casing along and about an axis of anticipated shock and vibration forces. Preferably, there are a sufficient number of tab means to prevent movement of the electrode assembly inside the casing along and about a plurality of axes of anticipated shock and vibration forces.
2. Prior Art
Typical techniques used in the construction of electrochemical cells begin with a deep drawn metal can which is closed at its bottom end. The electrode assembly such as a jellyroll assembly is inserted into the can. Cell fabrication continues with connection of the electrode leads to the cell can and insulated terminal pin on the header. The header is then welded or crimped onto the deep drawn can to complete the basic cell. While this fabrication technique lends itself well to automated manufacturing, it does not allow for any mechanical stabilization of the electrode assembly other than operations performed at the top of the assembly prior to sealing the unit.
U.S. Pat. Nos. 3,625,766 to Purcell, Jr. et al. and 4,495,259 to Uba are both directed to batteries capable of withstanding impact and vibrational forces, however, they also do not provide a multiplicity of conductor tabs at opposed ends of the electrode assembly, as in the present invention. In particular, Purcell, Jr. et al. describes a storage battery comprising a plurality of positive plates and a plurality of negative plates disposed in alternating and parallel relationship. The negative plates are in part held in position by parallel grooves provided in the spaced apart side walls of the housing. Further, the opposite polarity plates are interconnected through a plurality of alternating shims formed of rigid insulating material. The grooves and alternating shims do not function in a similar manner as the plurality of electrode connections of the present invention.
The Uba patent describes an electrode plate support member comprising a comb-like portion having a series of tines interposed between projecting tabs associated with the respective polarity electrode straps. Again, the electrode plate support does not function in a similar manner as the plurality of electrode connections of the present invention.
U.S. Pat. No. 5,238,757 to Suzuki et al. discloses an alkaline storage battery having an upper current collector comprising a circular current collecting tab resistance-welded to the terminal edge of the positive electrode and a rectangular lead connecting between the upper current collector tab and a sealing cover for the battery casing. The negative electrode has a lower current collector comprising a circular collecting tab spot-welded to the terminal edge of the negative electrode and a tongue-shaped lead connected between the lower current collector tab and the bottom of the casing. This construction does not provide for a plurality of electrode connections at opposed ends of the electrode assembly.
U.S. Pat. No. 4,452,869 to DeMoully et al. describes a battery terminal comprising a base portion having an integral tab. When the electrode assembly is inserted into the casing, the outer end of the integral tab is captured between the casing and sidewall of the assembly. If desired, two of these tabs may be attached to one or both ends of the electrode assembly. However, with one of these battery terminals positioned at the upper portion of the sidewall of the electrode assembly, the motion of sliding the assembly in a downwardly direction into the casing will tend to remove the upper tab from its captured relationship.
It is therefore an object of the present invention to provide a multiplicity of electrical tab connections at opposed ends of the electrode assembly and connected to the cell casing. These multiple connections serve to stabilize the electrode assembly within the casing being subjected to stress and vibration forces due to the fact that either the upper or the lower tabs are in tension condition. Thus, by eliminating axial movement of the electrode assembly, the electrical tab connections do not experience compressive loads which can result in tab and cell failure.
These and other objects will become increasingly more apparent to those of ordinary skill in the art by reference to the following descriptions and to the drawings.